I've been searching for a fiberglass tank now for about 3 years, and finally found one. Should make for a perfect observatory. Inside diameter is 7'6", and overall length, minus the other domed end is 17'. The tank has nice 3" foam core reinforcement fiberglass that will make a perfect dome lip. I think I can incorporate some castors into a wooden block to get the dome rotating, without the use of some sort of steel hoop (hopefully).

Apparently the tank sat in this fellow's yard for almost 10 years as a storage container for odds and ends. I drove by this thing for close to 8 years now thinking that it would be a great observatory. When the leaves came off the treees this fall and I saw the hole in the end... Eurika!!!

Anyway. I've attached the "inside" photo in reference to the other end. I know domes are hard to come by, and originally I was going to cut the end off and toss it in the trash - if anyone wants this end for free, it's up for grabs. The hole is an odd shape - the guy I bought the tank from told me that they had to cut one of the ends out for transport, or it would still be considered a tank. It's almost the perfect size for a scope anyway. I think when a set of shutters would be made for the opening, any openings that fell outside the frame of the shutter could be patched up without too much work or difficulty. If interested, PM me here, and we can arrange for pick-up.

Great find! This should be an interesting build to follow. Keep us posted with pix, sketches etc. Give the other end to Scott H, he can patch the hole and make a domed gazebo for the observatory cluster.

You bet... Should start cutting on this thing next weekend. I might keep the other end for a portable trailer OB if this all works out. I DO know of another fiberglass tank that's available though if anyone's interested.

It sat in his yard for 10 years... It was a gasoline tank from a convienence store. He said that when the industry first started using fiberglass tanks, the sticks that were used to measure fuel levels daily, eventually would cause a leak from repeated dropping of the wooden stick into the tank (I for one remember using these sticks in my younger days in college and working at the local Penzoil station).

Anyway, he used to dig them out, crush them down, and toss them in the landfill. For some reason he kept this one.

I think I'll be introducing more harmful trace elements from the flat black paint I intend upon using inside (LOL), than will be eminated from it.

It's going to make a great observatory. The fiberglass was laid up in a mold, so I have a perfectly smooth exterior surface to work with. The manufacturer made two halves, then mated them together. The exteriorior ribs are a different story. Hopefully will be able to cover them with something easier on the eyes, but first, I've got to get into working order!

I've had a lot of use out of mine, but the biggest problem I've had, is to have it rotate easily and freely. I've done this part over at least three times, with varying degrees of success. It still gives me a bit of a hard time, especially in Winter. Do you have plans on what kind of roller mechanism you're going to use?

You are a lot more trusting than me. Given that gasoline definitely leaches into the fiberglass (Hydrolysis of Fiberglass) once exposed to open air it will most definitely outgas back into the surrounding environment. He said the tank sat empty and exposed to the open air for 10 years but I for one would not want to sit inside and encapsulated, surrounded by this. The cheapness of the raw material could be nothing compared to the potential risk. Obviously you are willing to take that risk. Better thee than me......

At the moment I'm planning on cutting the good dome off, then severing a 6 foot chunk of the body off for placement in the yard. I'm building a fairly large garage this year, so I may incorporate the OB into the roof of the garage, in-which case I'll build the walls of it with 2X stock, and utilize only the dome.

That should work pretty good because it still enables me to observe from a temporary spot in the yard, then when the time comes, I can yank the dome off the yard OB, and place it on the roof.

I haven't come up with a design for a rotational assy yet. Been looking at commercial units, and I like the in-line skate wheel idea. Will also need lateral wheels. First things first is to find out how out-of-round the dome end is, then I can work from there. I would think that I can get it back in true with the use of a laminated ply ring, using gussets for reinforcement, and the entire ring screwed into the base of the dome - the bottom layer of ply, I would think with use of floor-grade ply could be used as a bearing surface for the vertical rollers, and the inside edge could be used for lateral rollers.

The tank weighs somewhere on the order of 1000#. WOW Roger - the entire fiberglass tank that I got hold of is only 3/8" thickness. I bet that this dome weight is no more than a couple of hundred pounds! You guys got me thinking... May have to get the sawzall out tonight!

In most spots, my dome is around 1/4" thick. I think you'll find inline skate wheels will make your dome hard to turn. I tried those, I tried small casters, I tried 6" ball bearings, and have finally wound up with a dome ring, as you mention, but with a 1" X 3/16" flat bar, used as a track and used v-pulleys with ball bearings as a track support.

This is what I wound up with. It's still hard to turn in some spots, but this is the final revision (I will be building a ROR that will be completely shielded from local light pollution, and will be able to image for longer periods of time without having to worry about clear pictures of the inside of my dome :-) ).

Attached Files

Roger. Thanks for posting the pics! I checked out your page and saw the original bearing against ply - guessing that didnt work well? Ill need to findcout how much my dome weighs at present to see where im at, how many tollers for load capacity/rating, etc. I'll know more after this weekend.

Those are fantastic photos you have taken! Hope to get there myself someday. Going to hopefully invest in a Gemini II system for my G11 mount this year, plus get this OB built.

Cut the end off yesterday evening. Didn't take too long, and used a battery and a 1/2 with the sawzall. Weight is somewhere between 150 - 200 lbs, probably closer to 150# because I can get under it and carry it on my shoulders/upper back without too much difficulty.

I'll get it into the garage tonight and start looking at what I can do to lay out a rotational assy and a shutter. What dimensions would be optimal for a 12" SCT (allowing for upgrading to a 16" scope (light bucket)? Also, how far would I need to cut past zenith so as to not limit myself (would 20 degrees past zenith work)? I don't want to cut 180 degrees, horizon to horizon.

What the heck? I rotated it... LOL. Guess the wrong 180 deg! Did some looking today for shutter dims and found a schematic for a 10'6" dome. Sucked it into CAD today and shrunk it down and underlaid it to the dimensions of this dome. The 10.5' dome had a 43" shutter, and shrinking down puts this one at 30" width. The schematic also had a profile view, and overlaying this view gave 25 degrees past zenith. Anyone want to give opinions on the shutter size (good to go, or too big/small)? Definately dont want to have to redo the hole at a later date, but at the same time I have a lot of stray light where I live, so Im guessing the smaller the shutter size, the better, in this reguard (obviously there are optical minimums).

Mine is 28", and when I image with the 70mm, it's not too bad, but with the C8, I find it a bit narrow. I suppose it wouldn't be too bad with a fork mounted alt-az, but an eq mount has you looking across the shutter in some weird positions. Thing is with a small dome, there's a limit on how wide you can go without it being too wide.

Mine is 28", and when I image with the 70mm, it's not too bad, but with the C8, I find it a bit narrow. I suppose it wouldn't be too bad with a fork mounted alt-az, but an eq mount has you looking across the shutter in some weird positions. Thing is with a small dome, there's a limit on how wide you can go without it being too wide.

That's what I figured too... The bigger the hole, the less function it has as what it was intended for in the first place (at least in my case for the stray light). I'm going to try cutting the 30 inches and past zenith at 25 degrees. I think this will work OK.

I did some measuring last night and found that it's only out of round by 1/4 inch, which is astounding considering how much fiberglass will shrink.

I'll cut my shutter out over the weekend, and get it cleaned up of all the lichens and moss growing on it, as well as all the oxidized epoxy resin and loose fiberglass chop. You can see this where I started wire brushing in the attached pic. There is also a form seam from the lay-up when the manufacturer built the tank. It's a perfect center line to measure from, so everything will be nice and symetrical with the dome.

I may also start on the inner ring that will be the bearing surface for wheels to run on. My thoughts on the bearing surface would be to keep it square in shape to minimize distortion of the ring. My thought is, is to counter sink wood screws through the dome and into the ring, along with polyurethane glue.

I figured out the problem with the photos... It's MAC IOS5 incompatibility with Windows7. They come in flipped in emails from my IPhone, so I rotated them. They look fine from my computer but are upside down on iPad or iPhone! I'll fix this Monday when back at the IBM machine (sorry for the poor graphics)!

Today, I square cut the bottom edge of the dome by building a jig to fit over the reinforcement. I scribed a line around the circumference of the dome, and used a jigsaw with a diamond blade to trim the edge off. Hopefully this'll be square enough that I won't have issues with rotation later.

I also wire brushed the entire dome surface to remove all of the dirt and loose glass chop. Did this prior to scribing and cutting so it would be easier and truer.

Also cut out the shutter. Went with 30" x 7'4" to arrive at the dimensions I mentioned before.

Working ahead, I'm going to try the skate wheel route even though it was mentioned this may not be the easiest turning assy. I thought about using holesaw cut plywood wheels for this, but would need the bearings, and at $3-5 apiece, I'd need a bunch at a fairly large expense! Looked all over the Internet, and finally found my wheels and bearings from toysRus in the form of 2 pairs of in-line skates. The 2 pair came to $30... They were on sale for $20/pair, but the second pair would also be marked down an additional 50%, so all in at $30 for 16 wheels and so-so bearings.